Tiêu chuẩn iso 16784 2 2006

Microsoft Word C029612e doc Reference number ISO 16784 2 2006(E) © ISO 2006 INTERNATIONAL STANDARD ISO 16784 2 First edition 2006 01 15 Corrosion of metals and alloys — Corrosion and fouling in indust[.]

Reference numberISO 16784-2:2006(E)

Corrosion of metals and alloys — Corrosion and fouling in industrial cooling water systems —

Part 2:

Evaluation of the performance of cooling water treatment programmes using a pilot-scale test rig

Corrosion des métaux et alliages — Corrosion et entartrage des circuits

de refroidissement à eau industriels — Partie 2: Évaluation des performances des programmes de traitement d'eau de refroidissement sur banc d'essai pilote

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`,,```,,,,````-`-`,,`,,`,`,,` -ISO 16784-2:2006(E)

Foreword iv

Introduction v

1 Scope 1

2 Normative references 1

3 Terms and definitions 1

4 Principle 3

5 Reagents and materials 3

5.1 Water characteristics 4

5.2 Preparation of synthetic test waters using mother solutions 4

6 Apparatus 5

6.1 Temperature measurement 5

6.2 Circulation-rate monitor 5

6.3 Make-up, evaporation and blow-down measurement 5

6.4 Cooling tower 5

7 Test method 6

7.1 Procedure 6

7.1.1 Cleaning of the test assembly 6

7.1.2 Test tube preparation and pre-treatment 6

7.1.3 System water content 6

7.1.4 Procedure to fill the cooling water system 6

7.1.5 Heating the test tubes 7

7.1.6 Flow rate 7

7.1.7 Blow-down and half-life 8

7.1.8 Biocide treatment 8

7.1.9 Make-up water for cooling-tower use 8

7.2 Determination of analytical and control parameters 8

7.3 Test data reporting 9

7.4 Test termination 9

8 Assessment of results 9

8.1 Recording of cooling water quality 9

8.2 Treatment of the test tubes 9

8.3 Assessment of results on deposition and fouling 9

8.4 Assessment of results on corrosion 10

9 Test report 11

Annex A (informative) Test data sheet on the performance of cooling water treatment programmes 12

Annex B (informative) Further information on some methods of measurement and test 15

Bibliography 19

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`,,```,,,,````-`-`,,`,,`,`,,` -ISO 16784-2:2006(E)

Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies) The work of preparing International Standards is normally carried out through ISO technical committees Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2

The main task of technical committees is to prepare International Standards Draft International Standards adopted by the technical committees are circulated to the member bodies for voting Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights ISO shall not be held responsible for identifying any or all such patent rights

ISO 16784-2 was prepared by Technical Committee ISO/TC 156, Corrosion of metals and alloys

ISO 16784 consists of the following parts, under the general title Corrosion of metals and alloys — Corrosion

and fouling in industrial cooling water systems:

— Part 1: Guidelines for conducting pilot-scale evaluation of corrosion and fouling control additives for open recirculating cooling water systems

— Part 2: Evaluation of the performance of cooling water treatment programmes using a pilot-scale test rig

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`,,```,,,,````-`-`,,`,,`,`,,` -INTERNATIONAL STANDARD ISO 16784-2:2006(E)

Corrosion of metals and alloys — Corrosion and fouling in

industrial cooling water systems —

Part 2:

Evaluation of the performance of cooling water treatment

programmes using a pilot-scale test rig

1 Scope

This part of ISO 16784 applies to corrosion and fouling in industrial cooling water systems

This part of ISO 16784 describes a method for preliminary evaluation of the performance of treatment programmes for open recirculating cooling water systems It is based primarily on laboratory testing but the heat exchanger testing facility can also be used for on-site evaluation This part of ISO 16784 does not include heat exchangers with cooling water on the shell-side (i.e external to the tubes)

2 Normative references

The following referenced documents are indispensable for the application of this document For dated references, only the edition cited applies For undated references, the latest edition of the referenced document (including any amendments) applies

ISO 3696:1987, Water for analytical laboratory use — Specification and test methods

ISO 8407:1991, Corrosion of metals and alloys — Removal of corrosion products from corrosion test

specimens

ISO 8501-1:1988, Preparation of steel substrates before application of paints and related products — Visual

assessment of surface cleanliness — Part 1: Rust grades and preparation grades of uncoated steel substrates and of steel substrates after overall removal of previous coatings

ISO 11463:1995, Corrosion of metals and alloys — Evaluation of pitting corrosion

3 Terms, abbreviations and definitions

For the purposes of this document, the following terms, abbreviations and definitions apply

3.1

ATP

adenosine tri-phosphate, an active chemical present in living bacteria

NOTE ATP concentrations can be indirectly measured and are used as an indicator for the presence of biology in cooling water

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cooling water treatment

adjustment of cooling water chemistry by which corrosion and fouling can be controlled

3.6

cycles of concentration

ratio of the concentration of specific ions in the circulating cooling water to the concentration of the same ions

in the make-up water

3.7

heat rejection capacity

amount of heat that can be rejected by a cooling-tower system

3.8

half-life

time needed to reduce the initial concentration of a non-degradable and/or non-precipitable compound to

50 % of its concentration in the cooling water

L is the characteristic dimension of the flow system, expressed in metres (m)

V is the linear velocity, expressed in metres per second (m/s)

ρ is the fluid density, expressed in kilograms per cubic metre (kg/m3)

η is the fluid viscosity, expressed in kilograms per metre per second (kg/m/s)

3.11

surface temperature

temperature of the interface between the cooling water film and the heat-transfer surface, whether the surface

be the tube wall or the outside of a fouling deposit

3.12

TOC

total organic carbon

wall shear stress

shear stress of the fluid film immediately adjacent to the tube wall

NOTE The wall shear stress is expressed in N/m2

5 Reagents and materials

The cooling water composition of the test should reflect the likely service application For laboratory testing using synthetic water, only reagents of recognized analytical grade and only water complying with the minimum requirements of grade 3 of ISO 3696 shall be used

There are two main operating environments, which may be adopted The first is to use the make-up water as used in the specific cooling system on-site (a variation on this is to use synthetic make-up water), and concentrate it to the required number of cycles in the test system Annex A includes forms recommended for recording test conditions, compositions of make-up and recirculating water, and test results

The second approach involves using a synthetic water simulating the on-site circulating water for the required number of cycles The use of synthetic circulating water obviates the need to concentrate the synthetic water

to obtain the desired cycles of concentration This approach simplifies the test by avoiding the use of the pilot cooling tower

Synthetic circulating water will usually contain a higher level of dissolved ionic solids than corresponding natural water, thus making the synthetic water more corrosive

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`,,```,,,,````-`-`,,`,,`,`,,` -ISO 16784-2:2006(E)

5.1 Water characteristics

The natural or synthetic water(s) used should be characterized as specified in Table 1.This Table should be used to record compositions of both the circulating water and the make-up water, if used Turbidity, total silica, bacteria and ATP need only be measured for on-site waters

Table 1 — Composition of make-up and circulating cooling water

No Component Value Units

a The unit of measurement will depend on the test method

5.2 Preparation of synthetic test waters using mother solutions

Synthetic test waters are normally prepared in the laboratory at the time of use by mixing mother or stock solutions One mother solution contains the alkalinity The other mother solution contains the hardness and other salts required in the test water The composition of these two solutions is calculated so that, when the solutions are mixed in the proper proportion, they prepare either the circulating test water or an appropriate make-up water Typical mother solutions are shown in B.1 Alternatively, mother solutions may be prepared as concentrates and subsequently diluted with demineralised water

of electrically generated heat occurs through the heat-transfer tube wall into the circulating cooling water The materials-of-construction of the test assembly shall be chosen so as not to influence the composition of the test water Glass or plastic [(e.g., poly(vinyl chloride) (PVC), chlorinated poly(vinyl chloride) (CPVC) or poly(vinylidene fluoride) (PVDF)] are commonly used

From the cooling water reservoir, the cooling water is pumped through the heat exchanger section at a controlled flow rate If the heat transfer tubes are mounted in series, only one flow rate controller is required If they are mounted in parallel, one flow rate controller is required for each heat exchange tube Through partial evaporation of water in a cooling tower (6.4), the heat absorbed is subsequently released to the environment Alternatively, if a cooling tower is not required to concentrate make-up water, a closed cooling loop to extract heat is used In order to determine corrosion rates on non-heat-transfer surfaces, corrosion coupons (flush mounted probes) of the relevant metals in the system should be used

If the heat exchange tubes are mounted in parallel, simultaneous tests may be run by setting a different combination of surface temperature and flow rate for each heat exchange tube However, it is highly

recommended that all of the heat-transfer tubes be of the same metallurgical composition

6.2 Circulation-rate monitor

The circulation rate can be measured by use of a flow meter in the flow line, either preceding or following the heat exchange tubes

6.3 Make-up, evaporation and blow-down measurement

A means for measuring the mass flow of make-up, the amounts of evaporation and blow-down water (including minimum, average and maximum values) shall be established and shall be included in the test report In essence, blow-down and make-up rates can be monitored by water meters and the evaporation rate deduced Chemical feed may be based on blow-down or make-up Blow-down is normally controlled using the conductivity of the circulating water Make-up is controlled by a level controller in the cooling-tower basin

6.4 Cooling tower

The design and heat rejection capacity of the cooling tower and tower fill are optional but shall be reported Deposition of salts in the cooling tower may occur depending on the system design An example of the apparatus is described in B.2 A visual inspection of the inside of the cooling tower at the end of the test is advised

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`,,```,,,,````-`-`,,`,,`,`,,` -ISO 16784-2:2006(E)

7 Test method

7.1 Procedure

7.1.1 Cleaning of the test assembly

Before starting a test, the test assembly shall be cleaned in order to prevent contamination with products from

a possible previous test or undesirable microbiological fouling

The following cleaning solutions are suggested: first, flushing with water, then flushing out with an appropriate solution, such as hypochlorite solution in the case of slime formation, sulfamic acid or citric acid and EDTA solution in the case of iron and/or calcium deposits If an acid solution is used, the system should be flushed with water, neutralized and then flushed again with water until the pH is neutral

7.1.2 Test tube preparation and pre-treatment

Measure and record the length of the test tubes on a test data sheet

The surface state of the metal tubes under test will have a significant influence on corrosion and fouling The method of surface preparation shall ensure good repeatability and the surface shall be free of artefacts from the preparation process The surface preparation method used should adhere to the supplier's instructions for the product that is to be tested The following information is optional for the test procedure, but it is necessary

to adopt a standard pre-treatment and preparation procedure for the test tubes

a) Degrease the test tubes internally and externally with acetone

b) Subsequently, blast-clean the test tubes externally with abrasive to preparation grade Sa3 (in accordance

with ISO 8501-1) and to a roughness, Ra, of approximately 2,5 µm Alternatively, abrade using SiC paper

of grade P400 (For some metals with certain pretreatments, abrasion may not be appropriate.)

c) Clean the test tubes by blowing with compressed air and weigh, to at least an accuracy of 0,01 g, and install them in the tubes of the heat exchanger (6.1) Record the mass of each test tube on a test data sheet

d) The tubes may be tested with or without pre-treatment It is frequently considered desirable to test in both conditions, in order to determine quantitatively the value of pre-treatment Pre-treatment is accomplished

by continuous circulation of the pre-film solution, specified by the water treatment vendor through the test tubes at room temperature for a minimum of 48 h and a maximum of 72 h, with a circulation flow rate of at least 0,6 m/s and without heating

Pre-treatment of the test tubes may be carried out in the test assembly itself, or in a separate circuit connected to the test assembly

7.1.3 System water content

The total water volume of the cooling water reservoir, heat exchangers and piping of the system shall be measured and reported

7.1.4 Procedure to fill the cooling water system

7.1.4.1 Using synthetic circulating test water made from mother solutions (no cooling tower)

Mix mother solutions as described in 5.2 so as to achieve the required cooling water quality, the parameters of which are given in Table 1 Fill the cooling water reservoir with the synthetic water and the solution of chemical treatment additives in accordance with the supplier's instructions

Start the circulation pump and adjust it so as to achieve the required circulation flow rate (see 6.2) Drain off at least five times the water content of the heat exchanger section from the system to ensure removal of artefacts from surface pre-treatment Start the dosing device and set the dose level to the prescribed values

`,,```,,,,````-`-`,,`,,`,`,,` -ISO 16784-2:2006(E)

(see 7.1.9) Then allow the cooling water to circulate normally, set the heater to the selected value of heat input, and balance this with the heat extracted in the cooling circuit Once this has been achieved, record the

time as the starting time of the test (t = 0)

NOTE It is desirable to have set-up the test rig and controls to establish the required steady state-conditions using dummy heat-exchanger test tubes, before starting a proper test run

7.1.4.2 Using make-up water (cooling tower required)

In this case, the make-up water (either by mixing synthetic mother solutions or using make-up water obtained on-site) is concentrated by evaporation in the model cooling tower to achieve the required composition before the start of the test period

Fill the cooling water reservoir with the make-up water and the solution of chemical treatment additives in accordance with the supplier's instructions Start the circulation pump and adjust it so as to achieve the required circulation flow rate (see 6.2) Drain off at least five times the water content of the heat exchanger section from the system prior to this water reaching the cooling tower to ensure removal of artefacts from surface pre-treatment

Set the heater to the selected value of heat input and monitor the conductivity of the water until the correct cycles of concentration are obtained Then start the blow-down pump and adjust to the appropriate blow-down rate (see 6.3) Start the dosing device and set the dose level to the prescribed values (see 7.1.9) Then allow the cooling water to circulate normally, set the heater to the selected value of heat input and record the time

as the starting time of the test (t = 0)

NOTE It is desirable to have set-up the test rig and controls to establish the required steady-state conditions using dummy heat-exchanger test tubes, before starting a proper test run

7.1.5 Heating the test tubes

The duty of the heating elements and the heat flux used should be chosen to represent particular service conditions A suitable apparatus is described in B.3

7.1.6 Flow rate

The recirculation flow rate measured in the circuit external to the heat-exchange tube section by the flow meter (6.2) shall be set high enough so that no overheating of test tubes occurs but not too high so that excessive turbulent water flow occurs within the tubes (A flow rate of 0,6 ± 1 m/s has been found to be suitable.)

The flow rate and Reynolds number along the test surface shall be determined

The following procedure shall be used as an option to set the flow rate: the cooling water velocity (volumetric flow rate) in the annular space along the test tubes can be calculated by the formula

φcirc is the circulation flow rate, expressed in cubic meters per second (m3/s);

v is the average cooling water velocity in the annular space, expressed in metres per second (m/s);

D is the internal diameter of the glass tube, expressed in metres (m);

d is the external diameter of the metal test tube, expressed in metres (m)

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